1. Field of the Invention
The present invention relates to compressed coded data transmitting systems, and more particularly to an apparatus for packetizing layer-coded video data and for transmitting it.
2. Description of the Related Art
In the transmission of video data, a system is known which divides coded data which contains DCT (Discreet Cosine Transform) components into low and high frequency component data and packetizes them individually in a H.261 encoding system which is an international standard for video conference, as described in JP-A-10-23418 laid-open on Jan. 23, 1998. In this invention, if data to be transmitted comprises low frequency components, a flag indicative of high priority is annexed to a packet for transmitting the data whereas if the data contains high frequency components, a flag indicative of low priority is annexed to the data for transmitting purposes. A gateway (which is a packet video speed converter capable of converting a video stream speed) disposed on a network discards the packets to which the flag indicative of low priority is annexed (high frequency component data) when the network becomes congested, alleviate the congested state of the network to thereby prevent a deterioration in the video quality.
For example, xe2x80x9cEncoding, Transmitting, and Controlling System in Video Multicastxe2x80x9d, The Journal of the Institute of Image Information and Television Engineers, Vol. 52, No. 6, pp. 863-870(1998-6) describes a layer-coded data transmission controlling system in which layer-coded video data is transmitted from a sever to a client in a multi-channel system using an IP address, transmit/receive code port numbers, etc. In this system, a total of six kinds of encoded data of low and high frequency components of respective I, P and B frame data, which an MPEG encoding system (Generic Coding of Moving Pictures and Associated Audio: Video, ISO/IEC 13818-2) which is an international standard prescribes for layering the video data, are transmitted from the sever to the client, using a plurality of channels. In order to reproduce the P frame data among the I, P and B frame data which the MPEG encoding system prescribes, the I frame data is required. In order to reproduce the B frame data, the I and P frame data are required. As a result, the respective decreasing significances are placed on the I, P and B frames in this order. The low frequency components of each frame which represent its basic contour are important compared to its high frequency components which represent the details of the frame. There are a total of six leveled significances, inclusive of those of the I, P and B frame structures. By transmitting those six leveled data, using a plurality of channels, only data for a layer which the client requests can be transmitted.
JP-A-6-339137 laid-open on Dec. 6, 1994 describes on its front page that xe2x80x9can image signal is packetized in packet assembling section 13 for each layer and is transmitted from transmitting section 14.xe2x80x9d
JP-A-3-22780 laid-open on Jan. 31, 1991 describes on page 4, lower right column, line 18xe2x80x94page 5, upper left column, line 2 that xe2x80x9ca first group of packets are formed of those image signal components, loss of which will cause a small extent of degradation of image quality and a second group of packets are formed of those image signal components, loss of which will cause a large extent of degradation of image quality, and a high priority is given to the second group of packets so that discard of the second group of packets is hardly effected.xe2x80x9d
JP-A-2-58938 laid-open on Feb. 28, 1990 describes in its claim that xe2x80x9cmeans for layer-structuring the coded information into basic blocks for decoding and into additional blocks for interpolating them and thereafter packetizing the resulting information for transmissionxe2x80x9d.
JP-A-2-86241 laid-open on Mar. 27, 1990 describes in its claim that xe2x80x9ccoded information is layer-structured into those portions which will exert small influence on the image quality and into those portions which will exert large influence on the image quality, and several blocks are formed into a packet for each portionxe2x80x9d.
JP-A-6-125361 laid-open on May 6, 1994 discloses a speech packet communication system intended to suppress degradation of speech quality when a packet is discarded.
JP-A-4-83488 laid-open on Mar. 17, 1992 discloses use of the layer-coding technique and the burst error correction technique in an ATM image signal transmission.
Since video data of a plurality of layers are transmitted through a plurality of channels in the conventional system, channels whose number equals the product of the number of video programs to be transmitted and the number of program layers are required. Thus, a plurality of addresses and ports are be consumed to transmit one video program.
When packet discarding occurs due to congestion of the transmission network, disordered packet discarding would lead to discard of data important for video reproduction, which can greatly affect the video reproduction. It is preferable that as described above with reference to the prior art, the I, P and B frame structures and the significances of the frequency component data are used to positively discard the component data, starting with the least significant component data when the network is congested. When one-video program data of a plurality of layers is transmitted through one channel in packets where components data belonging to different layers, for example, the low and high frequency components data of the B frame, are present in a mixed state, a router which has a packet discarding function in the network cannot discard only the high frequency component data of the B frame.
It is therefore an object of the present invention to provide a layer-coded video data transmitting apparatus where one-video program data of a plurality of layers is transmitted through one channel, and a router which has a packet discarding function in the transmission network can discard only specified layer data.
In order to solve the above problems, according to one aspect of the present invention, there is provided a layer-coded data transmitting apparatus for transmitting layer-coded data in a single channel, which apparatus packetizes layer-coded data so that a packet for transmitting the layer-coded data contains only data belonging to the same layer.
According to another aspect of the present invention, there is provided a layer-coded data transmitting apparatus for transmitting layer-coded data in a single channel, which apparatus divides into low and high frequency component data each of intra-coded image (hereinafter referred to as xe2x80x9cI framexe2x80x9d) data, prediction-coded image (hereinafter referred to as xe2x80x9cP framexe2x80x9d) data, and bidirectional prediction-coded image (hereinafter referred to as xe2x80x9cB framexe2x80x9d) data, which a video signal compressing/encoding system prescribes; and transmits in different packets the respective low and high frequency component data of each of the I, P and B frame data.
According to still another aspect of the present invention, there is provided a layer-coded data transmitting apparatus for transmitting layer-coded data in a single channel, comprising means for converting data belonging to each of layers of an elementary stream (hereinafter refereed to as xe2x80x9cESxe2x80x9d) to packetized elementary stream (hereinafter referred to as xe2x80x9cPESxe2x80x9d) data, and wherein the converting means converts the ES data so that only ES data belonging to the same layer is contained in a single PES packet. The apparatus further comprises means for packetizing the PES packet to a real time protocol (hereinafter referred to as xe2x80x9cRTPxe2x80x9d) packet for each layer data, so that only the RTP packet data belonging to the same layer is contained in a single RTP packet which transmits the RTP packet; means for packetizing the RTP packet to a user datagram protocol (hereinafter referred to as xe2x80x9cUDPxe2x80x9d) packet for each layer data, so that only the RTP packet data belonging to the same layer is contained in a single UDP packet which trasmits the UDP packet; and means for packetizing the UDP packet to an internet protocol (hereinafter referred to as xe2x80x9cIPxe2x80x9d) packet for each layer data, so that only the UDP packet data belonging to the same layer is contained in a single IP packet which transmits the IP; packet.
According to a further aspect of the present invention, there is provided a layer-coded data transmitting apparatus for transmitting layer-coded data in a single channel, comprising: means for converting layer-coded data belonging to each of layers of an elementary stream (hereinafter refereed to as xe2x80x9cESxe2x80x9d) to packetized elementary stream (hereinafter referred to as xe2x80x9cPESxe2x80x9d) data; first packetizing means for packetizing the PES data to a real time protocol (hereinafter referred to as xe2x80x9cRTPxe2x80x9d) packet for each layer data; and second packetizing means for packetizing the RTP packet to a user datagram protocol (hereinafter referred to as xe2x80x9cUDPxe2x80x9d) packet for each layer data, and wherein: the converting means converts the ES data so that only ES data belonging to the same layer is contained in a single PES packet which transmits an ES data; the first packetizing means divides the PES packet belonging to the same layer into a plurality of RTP packets, each of which includes the divided PES packet data and a RTP header annexed to the divided PES packet, so that the length of the RTP packet is not more than a maximum data length in which the UDP packet is transmittable; and the second packetizing means packetizes the RTP packet so that only the RTP packet data belonging to the same layer is contained in a single UDP packet.
According to a still further aspect of the present invention, there is provided a layer-coded data transmitting apparatus for transmitting layer-coded data in a single channel, comprising: means for converting layer-coded data belonging to each of layers of an elementary stream (hereinafter refereed to as xe2x80x9cESxe2x80x9d) to packetized elementary stream (hereinafter referred to as xe2x80x9cPESxe2x80x9d) data; and means for packetizing the PES packet to a user datagram protocol (hereinafter referred to as xe2x80x9cUDPxe2x80x9d) packet for each layer data, and wherein: the converting means converts the layer-coded data so that only the elementary stream data belonging to the same layer is contained in a single PES packet; and when the packetizing means divides the PES packet data belonging to the same layer into a plurality of UDP packets, said packetizing means annexes at a predetermined position in each of the UDP packets information representing a position of a datagram of that divided UDP packet in the undivided PES packet.
According to a further aspect of the present invention, there is provided a layer-coded data transmitting apparatus for transmitting layer-coded data in a single channel, which apparatus packetizes layer-coded data so that an internet protocol (hereinafter referred to as xe2x80x9cIPxe2x80x9d) packet for transmitting the layer-coded data contains only data belonging to the same layer; and transmits the IP packet.
According to a still further aspect of the present invention, there is provided a layer-coded data transmitting apparatus for transmitting layer-coded data in a single channel, which apparatus divides into low and high frequency component data each of intra-encoded image (hereinafter referred to as xe2x80x9cI framexe2x80x9d) data, prediction-encoded image (hereinafter refereed to as xe2x80x9cP framexe2x80x9d) data, and bidirectional prediction-encoded image (hereinafter referred to as xe2x80x9cB framexe2x80x9d) data, which a video signal compressing/encoding system prescribes; and forms an internet protocol (hereinafter referred to as xe2x80x9cIPxe2x80x9d) packet which transmits only each of the low and high frequency component data of each of the I, P and B frames; and transmits the respective IP packets.